Photosynthesis, Algae, CO 2 and Bio-Hydrogen John R. Benemann - - PowerPoint PPT Presentation

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GCE P E nergy Workshop

April 27, 2004, Alumni Center, Stanford University

Biomass E nergy

GCE P E nergy Workshop

April 27, 2004, Alumni Center, Stanford University

Biomass E nergy

Photosynthesis, Algae, CO2 and Bio-Hydrogen

John R. Benemann

Institute for Environmental Management, Inc. (Not for profit) Palo Alto and Walnut Creek, California jbenemann@aol.com

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200,000 ton Anaerobic Bioreactor Landfill

Davis, N. California (IE M, Inc. and Yolo County, 2004)

200,000 ton Anaerobic Bioreactor Landfill

Davis, N. California (IE M, Inc. and Yolo County, 2004)

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Photosynthesis, Microalgae and H2 Production Photosynthesis, Microalgae and H2 Production

Photosynthesis drives a carbon cycle that is 1 to 2 orders

• f magnitude greater than the fossil C cycle.

Microalgae have been studied for over 50 years as potential sources of foods, feeds, fertilizers and fuels, based in large part on their reputed ability to efficiently convert solar energy into chemical energy, either CO2 into biomass or even directly into hydrogen. THIS TALK ADDRESSES THE HOPE AND THE HYPE.

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Light-induced electron-transfer steps in PS II

(Red arrows: when the central pigments are excited by

light they share the excitation (Science, March 04)

Light-induced electron-transfer steps in PS II

(Red arrows: when the central pigments are excited by

light they share the excitation (Science, March 04)

Water Splitting and O2 producing Mn Center

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Bessel Kok, 1973 Bessel Kok, 1973

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E ffect of high light intensity

• n pigment

Content E ffect of high light intensity

• n pigment

Content

Dunaliella salina High Light

• n left

(yellow) Low Light

• n right

(green)

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f f

.

From Neidhardt, Benemann and Melis, 1998

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• 20

20 40 60 80 100 400 800 1200 1600 2000 2400 2800 3200

Light-saturation Curves of Photosynthesis Light-saturation Curves of Photosynthesis

Oxygen evolution mmol O

2 (mol Chl)

• 1 S-1

WT Chl def. Chl b-less

Chlamydomonas reinhardtii Mutants,

• Dr. J. Polle, Brooklyn College

Light Intensity, µE m-2 s-1

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Next Step: Outdoor Testing

• Dr. J. C. Weisaman, SeaAg, Inc. Vero Beach, FL

Next Step: Outdoor Testing

• Dr. J. C. Weisaman, SeaAg, Inc. Vero Beach, FL

WT Mutant CM2

Generation mutants of strains that can grow outdoors (Prof. Polle)

Diatom Cyclotella

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MICROALGAE R&D PONDS IN ROSSWE L, NE W ME XICO MICROALGAE R&D PONDS IN ROSSWE L, NE W ME XICO

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Typical High Rate Pond Design Typical High Rate Pond Design

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Microalgae Production Plant

in Hawaii (Cyanotech Corp). Red ponds for Haematococcus production, others cultivate the cyanobacterium Spirulina (known to produce H2 and candidate for indirect biophotolysis process)

Microalgae Production Plant

in Hawaii (Cyanotech Corp). Red ponds for Haematococcus production, others cultivate the cyanobacterium Spirulina (known to produce H2 and candidate for indirect biophotolysis process)

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International Network on Biofixation of CO2 and Greenhouse Gas abatement with Microalgae

EPRI EPRI

Rio Tinto Rio Tinto TERI (India) TERI (India) PNNL PNNL

Arizona Public Services Arizona Public Services

ENEL Produzione ENEL Produzione Ricerca

Ricerca Gas Technology Institute Gas Technology Institute

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• St. Helena, CA Wastewater Treatment Ponds
• St. Helena, CA Wastewater Treatment Ponds

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Antenna Size and Photosynthetic Efficiency

Photosynthetic Electron-Transport Chain 200 Chl 20 20 20 20 20 20 20 20 20 20 Photosynthetic Electron-Transport Chains

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SOLAR E FFICIE NCY TRAIN FOR PHOTOSYNTHE SIS SOLAR E FFICIE NCY TRAIN FOR PHOTOSYNTHE SIS

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Standard / Optimistic assumptions re. losses in photosynthesis

Incident Solar Radiation Percent Percent Factors Limiting Photosynthesis Lost Remaining Restricted to Visible Radiation 55 45 Losses to reflection, inactive absorption 20 / 10 36/40 Efficiency of primary reactions of PS 75 / 70 9 / 12 Respiration and dark metabolism 33 / 15 6 / 10 Light saturation and photoinhibition 50 / 10* 3 / 9 * 10% Loss assumes overcoming these limitations (see next slides) 1% Efficiency is about 33 t/ha/yr dry weight biomass production. Maximum is about 100 (higher plants) to 300 (microalgae?) t/ha-yr

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Solar energy is diffuse, its energy content is low!!

At a very favorable location: 5 kWh/m2/day = 6.6 GJ/year Under optimistic assumptions:

• 10% conversion efficiency
• $15 per GJ --> $10 H2/m2/year

A AA more realistic assumptions:

• 3 % conversion efficiency
• $5 per GJ (based on current $30/barrel crude oil)

→ $1 H2/m2/year

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INTRODUCTION TO PHOTOBIOLOGICAL H2 PRODUCTION INTRODUCTION TO PHOTOBIOLOGICAL H2 PRODUCTION Many different photobiological H2 production processes – both direct and indirect, single and two stage, microalgae or photosynthetic bacteria, have been studied for 30+ years. No practical applications have resulted. Some processes even lack a laboratory demonstration of the proposed reaction. For one example: “direct biophotolysis”, which produces H2 directly from H2O without intermediate CO2 fixation. Direct biophotolysis is the “Holy Grail” of H2 production, due to its perceived high efficiencies. Major projects

• ngoing at several National Labs, GCEP /Stanford U.,

UC Berkeley, TCAG/IBEA, others in U.S. and abroad.

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March 2004, National Academy Sciences: “The Hydrogen E conomy: Opportunities, Costs Barriers and R&D Needs”

Advanced Direct Photobiological H2 Production

March 2004, National Academy Sciences: “The Hydrogen E conomy: Opportunities, Costs Barriers and R&D Needs”

Advanced Direct Photobiological H2 Production

“H2 production by direct cleavage of H2O mediated by photosynthetic microorganisms, without intermediate biomass formation, [direct biophotolysis] is an emerging technology at the early exploratory stage… theoretically more efficient than biomass gasification by 1 or 2 orders of magnitude.” “…bioengineering efforts on the light harvesting complex and reaction center chemistry could improve efficiency several- fold... into the range of 20 -30 percent” (solar to hydrogen) ...“substantial fundamental research needs to be undertaken…” This presentation addresses the realism of these projections which are typical of claims and publicity for such processes.

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SCHE MATIC OF DIRE CT BIOPHOTOLYSIS

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FROM Benemann et al (1973): H2 E VOLUTION BY A CHLOROPLAST-FE RRE DOXIN-HYDROGE NASE RE ACTION

(IN VITRO DIRE CT BIOPHOTOLYSIS RE ACTION]

FROM Benemann et al (1973): H2 E VOLUTION BY A CHLOROPLAST-FE RRE DOXIN-HYDROGE NASE RE ACTION

(IN VITRO DIRE CT BIOPHOTOLYSIS RE ACTION]

_____________________________________________________________________________

Assay Contents umoles H2/15 min ________________________________________________________ Basic System (spinach chloroplasts, ferredoxin, Hase) 0.25 " " + DCMU (inhibitor of O2 evolution) 0.00 " " - Light (dark) 0.00 " " + glucose + glucose Oxidase (O2 absorber) 1.21 " " + glucose + glucose oxidase + DCMU 0.00 Heated Chloroplasts 0.01

_______________________________________________________________

CONCLUSIONS: Reaction is very short lived (<20 min) and VERY sensitive to even the small amounts of O2 produced in the process (with O2 absorber reaction runs >hours)

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PROBLEM #1 OF DIRECT BIOPHOTOLYSIS:

O2 produced by PS inhibits H2 production

PROBLEM #1 OF DIRECT BIOPHOTOLYSIS:

O2 produced by PS inhibits H2 production

The data from Benemann et al., 1973, shows that the O2 produced by photosynthesis strongly inhibits H2 production, at well below 0.1% O2 (< 30 ppb O2 ) This is at least 1,000-fold below what is required! Inhibition is not due to O2 inactivation of hydrogenase (Hase). Inhibition is due to the reaction of O2 with the electron transfer system (e.g. ferredoxin or in Hase).

Development by biotechnology of an O2 stable Hase reaction is NOT plausible (on thermodynamic and other grounds).

O2 absorbers (e.g. glucose-glucose oxidase) not practical –

photosynthesis needed to produce the O2 absorbers.

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DIRE CT BIOPHOTOLYSIS: ME CHANISM AND ISSUE S

Simultaneous, single-cell, single stage, H2 and O

2 Production

DIRE CT BIOPHOTOLYSIS: ME CHANISM AND ISSUE S

Simultaneous, single-cell, single stage, H2 and O

2 Production

O2

H2O PSII PSI Ferredoxin Hydrogenase H2

The fundamental problems of direct biophotolysis are:

• 1. The strong inhibition by O2 (from water) of H2 evolution.
• 2. The high cost of photobioreactors (to capture light and H2).
• 3. The production of highly explosive H2:O2 mixtures.
• 4. The low practical efficiency of all photosynthetic processes.

There are no plausible solutions to problems 1 to 3 (discussed next, Problem 4 was discussed above)

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PROBLE M # 2 OF DIRE CT BIOPHOTOLYSIS:

High Cost of Photobioreactors.

PROBLE M # 2 OF DIRE CT BIOPHOTOLYSIS:

High Cost of Photobioreactors.

Any process that uses light for H2 production must be contained inside a transparent photobioreactors For direct biophotolysis the photobioreactor must cover the entire area of the process. Photobioreactors are inherently expensive, due to major limitations in scale-up and unit sizes (< 100 m2). Photobioreactor costs will be well above $100/ m2 (even without cost of the tubes or other glazing materials). Photobioreactors are unaffordable even at the highest possible solar conversion efficiencies (10% solar to H2).

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E ARLY E XAMPLE OF PHOTOBIORE ACTOR FOR H2 PRODUCTION BY MICROALGAE (U.S., 1978)

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Tubular Photobioreactors in Hawaii designed for H2 Production (20 m long tube manifold, inclined at 5%)

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ALTE RNATIVE PHOTOBIOLOGICAL H2 PRODUCTION PROCE SSE S: INDIRE CT BIOPHOTOLYSIS ALTE RNATIVE PHOTOBIOLOGICAL H2 PRODUCTION PROCE SSE S: INDIRE CT BIOPHOTOLYSIS

The limitations of direct biophotolysis for H2 production led to proposals for “indirect biophotolysis” in which:

• 1. CO2 is first fixed into storage carbohydrates by

microalgae (e.g. starch in green algae, glycogen in cyanobacteria) growing in low-cost open ponds.

• 2. The accumulated polyglucose (starch, glycogen) is then

converted to H2 in a second anaerobic stage in the light in photobioreactors or in the dark in fermentation tanks. Separating the O2 and H2 producing reactions avoids O2 inhibition, greatly reduces the size of the photobioreactors (if any) and avoids production of explosive O2-H2 mixtures.

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First Indirect Biophotolysis Process used First Indirect Biophotolysis Process used

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N2-FIXING CYANOBACTE RIUM (NOSTOC) N2-FIXING CYANOBACTE RIUM (NOSTOC)

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Proposed Indirect Biophotolysis Process: Could use Spirulina, a mass cultured microalga Proposed Indirect Biophotolysis Process: Could use Spirulina, a mass cultured microalga

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Proposed Indirect Biophotolysis Process

(2nd Stage shown as a dark fermentation)

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C6H12O6 + 6 H2O 10 NADH + 2 FADH2 + 6 CO2

Photosynthesis (10% Solar Efficiency) 10 H2

Dark Fermentation (80-85% yield from Glu) H2O + CO2

hν

For high yields will need genetically engineered algal cell with high photosynthetic efficiency in producing carbohydrates and also high yields of H2 production in the dark by fermentations. THESE ARE THE R&D CHALLENGES OF PHOTOBIOH2

Indirect Biophotolysis with Dark Fermentation as 2nd Stage with high H2 yield - Schematic